Aramid fiber is aromatic polyamide fiber known as NOMEX (trade name of du Pont for meta-aramid or m-aramid fiber), which is excellent in electric insulation, heat resistance, anti-chemicals, etc. Accordingly, it has been widely used as an insulating material.
Aramid-polyester laminates wherein aramid papers prepared by mixed-paper making forces of aramid fiber and aramid pulp are laminated and bonded with an adhesive as disclosed in patent documents Nos. 1 to 5.
In patent document No. 1, a prepreg sheet is disclosed wherein plasma-treated aramid films, aramid non-woven cloth and semi-cured adhesive are united. In patent document No. 2, adhesive-free aramid laminate which is prepared by heat bonding aramid paper composed of m-aramid fibrid and heat resistive short fiber and polyethylene terephthalate film at 220 to 250° C. under a pressure of line pressure of 50 kg/cm or higher.
In patent document No. 3, there is disclosed a method of manufacturing aramid-polyester laminate wherein molten polyester is impregnated into aramid paper. In patent document No. 4, there is disclosed a method of manufacturing a laminate sheet by calendar treatment of m-aramid paper and polyester film.
The technology disclosed in patent document No. 1 has such problems that coating of adhesive or adhesive tape is necessary, and treatment of volatile solvent in the adhesive is necessary. In the technology disclosed in patent document No. 5 the prepreg is prepared by impregnating thermosetting resin into aramid fiber, wherein the thermosetting resin is a kind of adhesive.
On the other hand, technologies disclosed in patent document Nos. 2, 3 and 4 do not use adhesive, but polyester film or sheet and aramid fiber or aramid paper are laminated, then the polyester is melted and impregnated into the aramid fiber or aramid paper. In order to melt the polyester, the polyester must be heated at a temperature higher than a glass transition temperature. Accordingly, the cooled polyester re-crystallizes to decrease its elasticity.    (Patent document 1) Japanese patent laid-open 2003-246018    (Patent document 2) Japanese patent laid-open 07-032549    (Patent document 3) Japanese patent laid-open 07-299891    (Patent document 4) Japanese patent laid-open 08-099389    (Patent document 5) Japanese patent laid-open 11-209484